This invention relates to a sewing machine and in particular to a suction device associated therewith.
The type of sewing apparatus shown in the above identified patent is employed for the hemming of garments. Employed in combination with an apparatus of this sort is a machine which is commonly referred to as an overedge sewing machine. An inherent feature of overedge sewing machines, is that there is provided thereon a trimming mechanism which severs the marginal edge of a workpiece whereby forming a continuous residual strip which requires removal from the sewing area so as to not interfere with the subsequent stitching operation. As is also shown in the above identified patent, there is employed an edge guide mechanism which effectively guides one edge of the material workpiece into proper position relative the needle of the machine. It should be pointed out that in a hemming apparatus of type shown in said patent, guidance of the workpiece takes on special importance in that there is no manual dexterity employed once the hemming apparatus has begun its cycle.
It is well shown in the art of sewing machines in general, to position a suction tube on the underside of the workpiece support for drawing refuse from the stitching and trimming area. However, if a suction tube would be used, as suggested in the art, in combination with a mechanism of the type described in said patent the diameter of the suction tube could be limited to the dimensional area available on the underside of the work support plate. In view of the various mechanisms and apparatus which is situated about the workpiece support of the above identified patent, the dimensional area available on the underside of the support plate would require that the suction tube be limited to such an extent that the inlet opening of the tube could easily become jammed by the continual strip of material severed by the trimming mechanism.
In addition to this, most of the suction devices shown in the art have been employed to remove particles of debris, that is, thread chain cuttings, etc., and are usually situated rearward of the stitch forming instrumentalities. Most of the heretofore known suction devices have not been utilized for removing a continuous residual strip of material from the area of the trimming mechanism and therefore the size of the suction tube diameter has not been an important factor. As is apparent, if a small diameter suction tube were utilized on the underside of the work surface in combination with a hemming apparatus as described in said patent other disadvantages occur. A smaller diameter tube results in a reduced vacuum area and therefore requires a higher degree of suction force for broadening the region of suction so as to be capable of drawing the continuous residual strip into the tube. However, this increase in vacuum may effect the guidance of the workpiece itself, which, as mentioned above, is of great importance in the operation of a hemming apparatus of this sort. That is, the guidance of the workpiece could be effected by the suction force drawing the severed marginal edge downward. Accordingly, that portion of the garment still fastened to the residual strip is drawn against a rearwardly extending finger which forms part of the guidance mechanism whereby creating frictional forces. The availability for placement of the suction tube on the underside of the work support dictates that the continuous residual strip travel in a path leading from the workpiece which is on one side of the trimming mechanism to the open end of the suction tube which is positioned on the opposite side of the trimming mechanism. In this manner the continuous residual strip could be drawn downward and against the sharp edge portion of the lower knife of the trimming mechanism whereby creating further frictional forces. The combination of the frictional forces, inherent with the finger and the lower knife, although slight, could result in the displacement of the remainder the workpiece relative the edge guide mechanism. This displacement is possible in view of the fact that there is no manual dexterity and therefore no correctional factors employed in guiding the workpiece to the stitching mechanism. In a bottom hemming apparatus of the type described in said patent the guiding of the workpiece is mechanically manipulated at the onset of the cycle and the sewing machine is automatically operated thereafter. In view of the frictional forces operating on the workpiece during the sewing cycle it is possible that the workpiece would become misguided relative the edge guiding mechanism whereby resulting in the production of an unacceptable garment. For the reasons discussed hereinabove, the art heretofore known does not readily lend itself in combination with an apparatus as described in the above identified patent.